Wheel Rail Rolling Contact

Wheel has a continuous single point contact in the time forms a straight line. The wheel center is given by a straight line parallel to the foundation, passing through permanent center of rotation. So, the wheel rail contact force has no contribution originating from the wheel inertia in vertical direction. The change in the contact point forms no more a straight line in the time domain. This occur due to any irregularities in the wheel rail interface. Irregularity can occur either on rail or on the wheel.